(1) Field of the Invention
The present invention relates to an operable sealing mechanism for a strapping band, which is housed in a band type strapping machine to wind a strapping band around an article to be strapped and carry out a cutting and bonding operation for the strapping band.
(2) Description of Related Art
In band type strapping machines, an article to be strapped is strapped with a strapping band by annularly placing the strapping band around the article on a table, winding the strapping band around the article and carrying out the cutting and bonding operation. In some cases, an arch member is provided on the table to guide the strapping band for annularly placing the strapping band.
In order to wind the strapping band around the article and carry out the cutting and bonding operation, the operable sealing mechanism housed in a band type strapping machine includes a first gripper for holding a top end of a strapping band annularly placed around an article to be strapped; a band driving roller for feeding out the strapping band and winding the strapping band around the article by pulling back the strapping band to tension the strapping band when the top end of the strapping band is held; a second gripper for holding a rear portion of the strapping band wound around the article to keep the strapping band wound around the article; and a compression head for cutting the rear portion of the strapping band, and pushing and bonding (melt-bonding in most cases) the top end and the rear portion together, the strapping band being kept wound. The band driving roller is configured to be rotated by a band driving motor. The first gripper, the second gripper and the compression head are configured to be operated by driving cams, which are carried on a shaft for sealing rotated by a motor for sealing.
The band type strapping machine thus constructed is expensive since the machine includes two electric motors, i.e., the band driving motor for driving the band driving roller and the motor for rotating the shaft for sealing to operate the driving cams. In order to provide the band type strapping machine at low cost, it is preferable that the sealing mechanism is configured so that basic operations of the mechanism are carried out by a single driving motor.
It is an object of the present invention to provide an operable sealing mechanism for a strapping band, which is configured to be capable of operations up to the cutting and bonding operation, being free from trouble, without using plural driving motors.
In order to attain the problem, the present invention provides an operable sealing mechanism comprising a first gripper for holding a top end of a strapping band, which is annularly placed around an article to be strapped; a band driving roller for feeding out the strapping band and winding the strapping band around the article by pulling back the strapping band to tension the strapping band when the top end of the strapping band is held; a second gripper unit for holding a rear portion of the strapping band wound around the article to keep the strapping band wound around the article; and a compression member or a compression head for cutting the rear portion of the strapping band, and pressing and bonding the top end and the rear portion together, the strapping band being kept wound; the second gripper unit including an engageable pawl holding unit; the engageable pawl holding unit comprising an engageable pawl member provided so as to be swingable along a moving path for the strapping band; a holding member provided on an opposite side of the engageable pawl member across the moving path for the strapping band; and a spring unit for urging the engageable pawl member forwardly in a swinging direction so as to press a pawl tip against the strapping band; wherein the engageable pawl member allows the strapping band to be pulled back and prevents the strapping band from being fed out in a feeding direction by sandwiching and holding the strapping band between the pawl tip and the holding member when a force for feeding the strapping band in the feeding direction is applied to the strapping band. Even the band driving roller is stopped on completion of the operation for winding the strapping band around the article, and when the winding keeping function of the band driving roller to the strapping band is released, the strapping band wound around the article can be prevented from loosening since the strapping band can not substantially move in the feeding direction. Even when the pawl tip is pressed against the strapping band prior to completion of the operation for winding the strapping band around the article, the engageable pawl member is no bar to pull back the strapping band since the engageable pawl member is configured to allow the strapping band to move in a direction to pull back. The operable sealing mechanism is normally provided with a heater for melting the top end and the rear portion of the strapping band.
In accordance with the present invention, the engageable pawl member is urged forwardly in the swinging direction, i.e. in a direction to feed out the strapping band by the spring unit, and the pawl tip is pressed against the strapping band. More specifically, the pawl tip is pressed against the strapping band after the strapping band has been fed out. When the strapping band starts moving in the feeding direction, i.e., when the strapping band makes a slight movement, the pawl tip also moves along with the strapping band in the feeding direction to shift the engageable pawl member forwardly, i.e., in the feeding direction since the pawl tip is urged in the feeding direction by the spring unit to be pressed against and engaged with the strapping band. When the engageable pawl member shifts forwardly, i.e., the pawl tip projects into the moving path for the strapping band or further projects into the moving path to narrow the gap between the pawl tip and the holding member, sandwiching and holding the strapping band between the pawl tip and the holding member. Conversely, when the strapping band moves in the direction to pull back, the pawl tip also moves in the direction to pull back along with the strapping band to shift the engageable pawl member backwardly, i.e., in the direction to pull back. When the engageable pawl member is shifted backwardly, the strapping band moves in the direction to pull back, being in frictional contact with the pawl tip, since, e.g., the pawl tip is configured to get out of the moving path for the strapping band in this time. The holding member may be provided by a guide forming the moving path for the strapping band for instance. The strapping band may move along the guide, being in contact with a guiding surface of the guide or being in sliding contact with the guiding surface.
The first gripper and the compression member or the compression head may be configured to be operated by a holding cam and a bonding cam, respectively, which are carried on the shaft for sealing. The shaft for sealing may be configured to be rotated by use of a band driving motor as a driving force, the band driving motor rotating the band driving roller.
The second gripper may be formed only by the engageable pawl holding unit. The grip head of the second grip, which is operated by the holding cam carried on the shaft for sealing and moves toward an opposing member, such as a seal anvil, to sandwich the rear portion of the strapping band along with the opposing member, may be formed as the swingable engageable pawl member. In this case, the second gripper is operated by the holding cam to sandwich and hold the strapping band between the opposing member and the second gripper while the grip head functions as the engageable pawl member to prevent the strapping band from shifting in the feeding direction. However, in order to reliably and continuously hold the strapping band up to completion of the operation for cutting and bonding the strapping band, and to avoid malfunction during the operation for holding the strapping band, it is preferable that the engageable pawl holding unit is formed independently from the second gripper. From this viewpoint, it is effective that the operable sealing mechanism for a strapping band comprising a first gripper for holding a top end of a strapping band, which is annularly placed around an article to be strapped; a band driving roller for feeding out the strapping band and winding the strapping band around the article by pulling back the strapping band to tension the strapping band when the top end of the strapping band is held; a second gripper for holding a rear portion of the strapping band wound around the article to keep the strapping band wound around the article; and a compression member or a compression head for cutting the rear portion of the strapping band, and pushing and bonding the top end and the rear portion together, the strapping band being kept wound; an engageable pawl holding unit further provided on a rear side of the second gripper, i.e., on a side of the second gripper facing a direction to pull back the strapping band; the engageable pawl holding unit comprising an engageable pawl member provided so as to be swingable along a moving path for the strapping band; a holding member provided on an opposite side of the engageable pawl member across the moving path for the strapping band; and a spring unit for urging the engageable pawl member forwardly in a swinging direction so as to press a pawl tip against the strapping band; wherein the engageable pawl member allows the strapping band to move in the direction to pull back and prevents the strapping band from being fed out in a feeding direction by sandwiching and holding the strapping band between the pawl tip and the holding member when a force for feeding the strapping band in the feeding direction is applied to the strapping band.
The second gripper and the compression member or the compression head may be configured to be operated by a holding cam and a bonding cam, respectively, which are carried on the shaft for sealing. The shaft for sealing may be configured to be rotated by use of a band driving motor as a driving force, the band driving motor rotating the band driving roller.